GitLab

Support having multiple AuthStatusConsumer's in
ExistingUserController.

This is a preparation CL for implementing a browsertest that needs to
subscribe itself as a "consumer" without suppressing the default
consumer functionality (LoginDisplayHostMojo).

Bug: 1033936
Change-Id: I97e6869c105bcddc6263f6bc201ff370a03d41dd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2315336Reviewed-by: Denis Kuznetsov [CET] <antrim@chromium.org>
Commit-Queue: Maksim Ivanov <emaxx@chromium.org>
Cr-Commit-Position: refs/heads/master@{#791260}